The present disclosure relates to a spin flash dryer for producing a powder by spin flash drying in particular for use in the field of food waste disposal.
The disclosure specifically relates to spin flash dryer for drying of a material, in particular from the food processing industry, in the form of a paste or a filter cake, with a vertical, cylindrical, dryer chamber having a rotating coaxially placed stirrer, with a variable speed drive screw feeder and with apertures for supply of hot drying gas and for removal of the spent drying gas and removal of the dried material.
Feed material preferably dried according to the invention are organic materials, preferably organic waste materials such as e.g. food waste products, fruit and beet pulps, distillers' residues, waste products comprising animal blood such as e.g. slaughterhouse animal waste, proteins, carbohydrates such as e.g. sugars and starches, fatty waste, and non-caking permeates. Preferred organic waste materials are waste products comprising blood. The feed material can e.g. be a liquid suspension comprising a solids fraction, a paste, or a filter cake material, wherein a fraction of the liquid suspension comprising a solids fraction, the paste, or the filter cake material has a particulate size which is too large to undergo spin flash drying, i.e. which density is larger than the lifting power of the fluidization medium of the spin flash dryer, or alternatively wherein the solids fraction is formed during operation of the spin flash dryer by aggregation or agglomeration.
It is well known, e.g. from EP 0 141 403 to dry materials in the form of a paste or filter cake to obtain a powder. In this apparatus the produced powder particles sizes are all under a given cut size and the residual drying gas is furthermore emitted to the environment. Likewise it is well-known e.g. from WO 97/19307 to spin flash dry powder with a desired mean particle size and a narrow particle size distribution.
As spin flash drying has gained popularity the materials which have been dried in these dryers have increased in complexity and today it is not uncommon to attempt to dry materials, wherein the material to be dried can be formed into a paste or a filter cake, but wherein this material nevertheless comprises a fraction of the paste or filter cake material, that has a particulate size which is too large to undergo spin flash drying, or wherein a fraction of the material to be dried undergoes insufficient particulation during drying thereby forming agglomerates which cannot be lifted by the drying air and out of the spin flash dryer.
Such a situation is particularly often observed in the food processing industry, where the residual organic material supplied to the spin flash dryer often aggregates and agglomerates during spin flash drying, thereby forming agglomerates which accumulate at the bottom of the spin flash dryer. This is highly unwanted and has several undesired consequences, such as e.g. increasing residence time of the material in the spin flash dryer, reducing the spin flash dryer's capacity as well as decreasing the intervals between maintenance stops.
This situation in particular is often observed in the meat processing industry. Waste materials from meat processing often contain useful organic components which cannot be separated from the carcass of the animal body in the normal process of cutting and parting the animal. However, such waste materials from meat processing can be utilized in further industrialized process steps. For example meat processing by-products comprising an animal blood fraction are useful by-products of the meat processing industry which advantageously can be spin flash dried to obtain powders enriched in blood.
However, in pastes or filter cakes comprising a meat processing by-product comprising an animal blood fraction it is often the situation that the by-product also comprises a fraction of material, e.g. crushed bones from the animal carcass, which cannot undergo spin-flash drying and therefore accumulates at the bottom of the spin flash dryer, or, which is more common, particles of ligaments and sinews together with the ever present blood, coagulate and become gluey under the processing conditions of the spin flash dryer, and start forming very large, kg-scale, conglomerates of spin flash waste which cannot undergo spin flash drying. However, by authorities, and for economic reasons, the ability to correctly treat by-products of the meat processing industry comprising blood and crushed bones material is considered essential for health and environmental reasons.
In general, accumulation of material, in particular of waste materials buildup, at the bottom of a spin flash dryer is cumbersome to handle as removal of this material generally requires the processing line to be shut down during maintenance, which may entail disassembling the spin flash dryer and long waiting times in order for the dryer to cool to temperatures which permit operator access to the drying chamber. Also, when food products is concerned, operator access is highly unwanted as it will disturb (or contaminate) the biological integrity of the spin flash drying system.
There exists, therefore, the need for a spin flash dryer which can handle such agglomerating materials without requiring an increased number of maintenance stops.
WO 03/018954 discloses a cuttings processing system including a steam atmosphere spin flash drying chamber able to process oil-enriched rock cuttings in an inert atmosphere for direct installation on an off-shore oil platform. The spin flash unit included in the cuttings processing system of WO 03/018954 includes a drain and overs discharge for access to the spin flash unit during operation down time. Spin flash drying of oil-enriched material is a particular dangerous process and the cuttings processing system is designed to stay closed during operation to prevent or reduce the risk of fire on the oil platform. Due to the manner in which oil is drilled, rock cuttings have uniform size distributions with only a minor fraction having a size which is too large to undergo spin flash drying. Further, rock does not undergo agglomeration. Rather, the rock fraction will accumulate, but not aggregate, at the bottom of the spin flash dryer and for safety reasons must be removed during intermissions for maintenance in the production line.
In the context of the present disclosure, waste material is to be understood as any matter contained in a feed material for a spin flash dryer, typically a paste or filter cake material, fed to a spin flash dryer, which waste material cannot undergo particulation and/or flocculation to become a dried spin flash product in a spin flash dryer and be lifted by the drying air flow against the gravitational force to exit the spin flash drying chamber through an aperture for removal of a dried spin flash product from the drying chamber of the spin flash dryer.
Such waste materials are routinely observed to form in many spin flash drying processes as residuals still contained in the drying chamber (1) after an interval of drying time otherwise considered sufficient for particulation and flocculation of the feed material.
In CN 202562247 (U) there is disclosed a drying unit, in particular a spin flash dryer, comprising a spin flash drying room, a dispersing device, a driving device, a revolving shaft, an air inlet and a feed inlet. The revolving shaft is connected with the driving device, the dispersing device is connected with the revolving shaft, and the dispersing device and the revolving shaft are arranged inside the spin flash drying room. The dispersing device comprises more than three dispersing vanes, and one end of the dispersing vanes is connected with the revolving shaft to form an annular dispersing surface. The spin flash dryer of the described invention is directed to effective avoidance of materials buildup on the bottom of a dryer through the dispersing device.
The present inventors have now realized the need for further improvements in spin flash dryers to overcome unwanted effects on the drying process and spin flash chamber due to residual organic waste material buildup on the bottom of such a spin flash dryer, in particular in the field of food processing, and most in particular in the field of waste products from the food processing industry comprising blood.